The present invention relates to an analysis of gaseous polar molecules, and, in particular, to a simple and high sensitive measuring method of injurious gas components for human health and to an apparatus for performing the same method.
It is well known that the polluted city air, factory exhaust smokes and/or the automobile exhaust gases include injurious substances for human health and the demand of detecting and measuring these substances with high sensitivity has been increased recently. For this purpose, the gas chromatography or the mass spectrometer has been utilized heretofore. In either of the conventional apparatus, however, considerably complicated operations are required to identify these substances contained by a very small amount in the sample gas having a very complex composition and to measure the amount thereof.
It has been known that most of the air polluting substances are polar molecules having dipole moments and have different energy absorption bands in the microwave region which are inherent to the respective molecules. One of the important features of the absorption in the microwave region is that it produces well resolved spectrum. Therefore, it is easy to identify and measure some very small amount of substance exactly from the position of absorption, i.e., absorption spectrum irrespective of the composition of the sample gas including the substance.
In the conventional gas analyser utilizing the microwave absorption, a waveguide cell or Fabry-Perot type resonator is used and the detection of spectrum is performed by sweeping microwave frequency. In the case of the waveguide cell, the length thereof must be at least several meters in order to obtain a sufficiently high detection sensitivity. However, since it is not practical to produce and to use such long cell, the sensitivity could not be obtained accordingly. The Fabry-Perot type resonator is essentially larger in size than the cavity resonator. In the latter case complicated apparatus and/or complicated regulations of the apparatus are usually required to provide an appropriate frequency sweeping.